The invention relates to an arrangement for supplying cooling air to a turbine casing, especially that of an aircraft gas turbine, and comprising at least two cooling-air pipes or ducts branching off from a compressor stage, one pipe opening into the wall space of the turbine casing and the other pipe extending through the wall space and opening into a mounting space for the turbine bearings.
An arrangement for supplying cooling air to a turbine casing and comprising a single cooling-air pipe is shown in U.S. Pat. No. 4,542,623. An arrangement with two cooling-air pipes according to the preamble of claim 1 herein constitutes close prior art, at least within our firm. Cooling-air pipes of this kind extend at least partly outside the turbine casing and may become damaged, for example, when the aircraft gas turbine is in operation. The object of the invention, therefore, is to provide means which always ensure at least an adequate cooling of the turbine casing, particularly the wall space and the space for the turbine bearings.
To this end, the second cooling-air pipe has at least one air overflow opening located in the wall space of the turbine casing. Other advantageous features are disclosed in the subclaims.
According to the invention, cooling air enters the wall space in the turbine casing not only through the first cooling-air pipe, which opens into the wall space, but also through the second cooling-air pipe, which is mainly for cooling the turbine bearings mounting spaced for which purpose it extends through the wall space. According to the invention, air overflow openings are formed in the second cooling-air pipe in the region of the wall space so that cooling air can flow out into the wall space. If, for example, there is a break in the first cooling-air pipe which opens into the wall space, cooling air can still enter the wall space through the second cooling-air pipe and the openings therein. If, however, the second pipe is broken and the first pipe is intact, cooling air can flow from the wall space through the overflow openings into the second pipe so that the mounting space for the turbine bearings in the turbine casing can still be supplied with cooling air. The air overflow opening or openings, which can for example be in the form of holes in the tubular second pipe, act as 3-way valves.
To obtain a uniform distribution of cooling air, and also for the purpose of redundancy, two cooling-air pipes of the first-mentioned kind and two cooling-air pipes of the second-mentioned kind can be distributed around the periphery of the turbine casing.
The above-mentioned advantages and other advantages of the invention will be clear from the accompanying drawing of a preferred embodiment.